Sheet making mechanism



May 27, 1947. KRATZ SHEET MAKING MECHANISM 3 Sheets-Sheet 1 Filed April26, 1943 [72 M97275? fczozzardfyl rafz.

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SHEET MAKING MECHANISM Filed April 26, 1943 3 Sheets-Sheet 2 1/ jfdouardfyfiazz y 194?. E. M. KRATZ 2,421,073

SHEET MAKING MECHANISM Filed April 2a, 1943 :5 Sheets-Sheet 5 mi "H jg I[III/Ill will! WWW w fdbzzarci/Yfizzi'i Patented May 27, 1947 SHEETMAKING MECHANISM Edouard M. Kratz, Gary, Ind., assignor, by mesneassignments, to Carbide and Carbon Chemicals Corporation, New York, N.Y., a corporation of New York Application April 26, 1943, Serial No.484,634

Claims.

This invention relates to improvement in sheet making mechanism and hasparticular reference to mechanism for delivering a film of liquid to asurface on which a Web of sheet material is to be formed.

Among the troublesome problems encountered in attempting to produce asheet of uniform thickness are those of preventing a more or lessautomatic build-up of thickness at the edges of the web (probably due tosurface tension characteristics of the liquid coating delivered to theforming surface) the elimination or prevention of the formatign ofripple-like effects incident to the travel of the liquid coating underthe edge of a doctor blade; the maintenance of uniformity of the depthof liquid coating and of resulting sheet thickness notwithstandingtemperature changes which cause warping of the conventional metal doctorblade; the drying of the liquid on the doctor blade adjacent itsoperative edge and resulting interference with normal function thereof;and the maintenance of a substantially constant temperature of theliquid and of the doctor blade to obtain uniformity in the sheetproduction.

The main objects of the present invention are to provide improvements inthe doctor blade and liquid depositing structure which will effectivelyovercome the difiiculties indicated in the foregoing statement oftroublesome problems.

In prior art structures of which I am aware, attempts have been made tosolve the indicated problems by relatively large, heavy and cumbersomehopper and doctor blade constructions which are also objectionablebecause of their excessively high cost.

It is also an object of the present invention to provide mechanism ofthe character indicated which will be of both simple and durableconstruction and which may be produced at very low cost.

Other objects and advantages will be understood by reference to thefollowing specification and accompanying drawings (three sheets) whereinthere is illustrated sheet forming mechanism embodying a selected formof the invention.

In the drawings:

Fig. 1 is a plan of an end portion of sheet forming mechanism to whichthe improved doctor blade structure is applied.

Fig, 2 is an end elevation.

Fig. 3 is a section on the line 33 of Fig. 1.

Fig. 4 is a section on the lines 4-4 of Figs. 1 and 3.

Fig. 5 is a section on the line 5-5 of Fig. 1.

Fig. 6 is a perspective of the improved doctor blade structure.

Fig. '7 is a perspective of the trough or hopper which is associatedwith the doctor blade for delivering liquid to the forming surface, and

Fig. 8 is a front elevation of the improved doctor blade.

The sheet or web forming mechanism herein disclosed embodies a sheetmetal band or belt H] which is supported by suitable rolls or drums, oneof Which i indicated at H. The drum H is carried by a shaft journalledin suitable bearings i2 supported by side frames l3 of the apparatus.The roll II is driven at the desired speed by any suitable means, hereinillustrated as including worm wheel l4 secured to the shaft of the drum,and a Worm gear l5 carried by a driven shaft [6 and operatively meshingwith the worm wheel I l. The drum II is preferably a hollow drum, and a,heating medium such as hot water is circulated through the drum formaintaining the drum and the forming belt [0 at a predeterminedtemperature. Hot water may be delivered to and may escape from the drumthrough the opposite end portions of the drum shaft, which may behollow. Suitable couplings such as indicated at I! may be provided forconnecting the necessary water piping to the ends of the drum shaft.

A doctor blade and liquid trough supporting frame It, embodying atransverse member l9 and longitudinally extending end arms 20, arepivotally mounted on a rod 2! which is suitably supported on the upperends of posts 22 which extend upwardly from the frames IS. The side arms20 of the member I8 are provided with rollers 23 rotatably mounted insuitable enlargements of the arms, and said rollers bear on the surfaceof the drum ll near its ends for supporting the member 18 insubstantially fixed operative relation to the surface of the drum and tothe surface of the forming band It].

A metal doctor blade 24 has end portions 2 5 (shown in this instance asbeing of reduced width) vertically slidably positioned in appropriatelyformed slots or ways 26 provided in upwardly extending enlargements 21of the arms 20. The main, if not the only, functions of the lastmentioned mounting of the doctor blade in the arms 20 are to support thedoctor blade in an approximately vertically disposed position and topermit raising or lowering of the doctor relative to said arms 20 whilepreventing any substanti q rocking of the doctor blade about an axisextending in the direction of the length of the doctor.

The doctor blade 24 is adjustably supported in selected positionrelative to the surface of the forming belt or band by means of a pairof rolls 28 which engage the surface of the roll H (see Fig. 4), and arerespectively associated with the opposite end portions of the doctorblade. Each roller 28 is mounted in the lower end of a clevis or forkedmember '29 which embraces the thickness of the doctor blade 24 (see Fig.and the doctor blade is vertically movable in said clevis. Guide bars30-30 arranged at the sides of the arms of the forked member and securedto the doctor blade, and cover plates 3| extending over the clevis armsand secured to said guide bars 3ll30, serve to hold the rollers andtheir mounting members 29 against lateral shifting or wobbling relativeto the doctor blade. Vertical adjustment of the doctor blade relative tothe band I0, is effected by means of a screw 32 which is threadedthrough the bar 24 so as to cause its lower end to engage the cross part33 of the roller mounting member 29. Turning of the screw in or out willefiect downward or upward adjustment of the roller. To facilitaterepeated setting of the doctor blade in predetermined spaced relation tothe band l0, the screw is provided with an adjusting arm 34 which servesas a pointer with reference to a suitable scale provided on an indexplate 35. Th index plate 35 is fixedly mounted on the upper edge of thedoctor blade 24 in any suitable manner.

The doctor blade 24 is preferably made of a very rigid and inflexiblemetallic bar, the lower edge of which is preferably beveled, asindicated at 36, to provide a thin lower edge portion 3l. The positionof the lower edge 31 relative to the surface of the band It! determinesthe: thickness of the coating of liquid L (Fig. 3) which is carriedforwardly by the band II]. By making the doctor blade 24 out of materialwhich has a very low and substantially negligible coefficient ofexpansion within the range of temperatures to which the doctor blade issubjected, I have found that it is practicable to more or less arch thelower edge of the bar longitudinally to a very slight extent for thepurpose of preventing a tendency of the liquid to increase its depth orthickness near the edges of the coating. As represented in Fig. 8, thelength of the lower edge 31 of the doctor bar has its central portion,indicated by the dimension line C, recessed slightly from the normalplane of said lower edge. The extent of recessing is ordinarily veryslight, usually only a matter of .001 or .002 inch. The end portions ofthe lower edge of the bar, such as indicated at D, incline downwardly tothe normal plane of said lower edge 31 and, if desired, short endportions E may continue outwardly in said normal plane. By suchformation of the lower edge of the doctor blade, the coating of liquidcarried forwardly on the band It] has its marginal portions slightlytapered to conform to the thinning effect of the downwardly inclinedportions D of the lower edge of the doctor blade. It has been found thatin the normal operation of the apparatus, the liquid coating has atendency to build up its thickness at its edges. This tendency may bethe result of some characteristic surface tension, or it may beotherwise explained. In any event, by initially forming the liquidcoating with margins of gradually reduced thickness as alreadyindicated, it has been found that the final sheet product will be freefrom thickened edges or margins. This is a highly important advantage inthe production of sheeting, first in that it avoids waste of materialincident to trimming away the objectionably thickened portions, eitherbecause the thickened margins will not meet the specifications of thefinished product or because satisfactory reeling of the web with suchthickened portions is difiicult to effect if not impracticable. It maybe observed that in attempting to reel sheeting in which the margins arethicker than the body of the sheet, the ends of the reel will build upto a much larger diameter than is required by the intermediate portionof the reel, thereby causing the reel to be too loosely woundintermediate its ends, too tight at its ends, and otherwise uneven andobjectionable.

When the doctor blade 24 is made of thermostable material such as abovealluded to, for example Invar steel, one commercial form of which isavailable under the trade name Fahralloy, the use of the described,slightly arched doctor blade edge is quite practicable in thatvariations in temperature and consequent changes in the blade due toexpansion or contraction will not occur to alter the operative edge ofthe bar.

I have found that a doctor blade made of the said Fahralloy containing37% nickel, a minor percentage of manganese (l /2%), and possibly 1% ofsilicon (the balance being iron), gives effective thermostability in therange of temperatures employed in the production of certain sheeting,the solution for which is preferably delivered to the forming band atabout F. It will, of course, be understood that the doctor blade shouldbe made of an alloy which provides the desired thermostabilitythroughout the temperature range which is experienced in the productionof a sheet from the particular solution to be employed.

The doctor blade 24 has detachably secured to it a trough-like structure38, preferably made of sheet metal and embodying a temperature controlchamber or jacket 39 at one side. The jacketed trough structure '38embodies a front wall 40, the height of which is somewhat less than theheight of the jacketed side of the trough. The liquid to be deposited onthe band I0 is introduced to the trough, preferably at about the centerthereof, through an inlet connection 4|. The trough has its ends closedby end walls 42, and the top wall 43 of the jacketed side thereof isextended rearwardly and then upwardly as indicated at 44 to form a smalloverflow tray. The ends of the trough are also preferably provided withwood or other end plates 45 suitably attached to the end plates 42. Hotwater or other temperature controlling medium may be circulated throughthe jacket 39, the heating medium being delivered to the jacket throughan inlet connection 46 and discharged through an outlet connection 41.

On the bottom of the trough or hopper 38 there is provided a pair ofdepending ribs 48 and 49, between which there is frictionally positioneda flannel, felt or similarly wrapped wood or like bar 50. The soft,non-scratching covering on the bar 50 rests on the highly polishedsurface of the band l0 and serves to support the hopper on the bandwithout danger of scratching the band incident to its travel under thehopper. The trough or hopper is detachably connected to the doctor blade24 by means of a pair of spring clips Sl-Sl which are secured to thedoctor blade and adapted to hook around the end members 45 of the troughstructure to thereby hold the latter in predetermined juxtaposedrelation to the doctor blade. The liquid material from which thesheeting is to be formed is delivered to the trough 38 at such a ratethat the trough is filled to a point considerably above the top edge ofthe front wall t0, the liquid overflowing said front wall 483 andfinding its way downwardly between said front wall 4!] and the doctorblade to be deposited on the band ill. The space between the front wall411 of the trough and the adjacent face of the doctor blade 24 iseffectively closed by portions of the side members 15 which extendforwardly from the front edges of the end members 42 of the trough intosubstantially abutting relationship to the adjacent wall of the doctorblade, in which position said end members 115 are held by the clips Theslight space beneath the lower edges of the end members 4'5, and betweenthe lower edge of the doctor blade and the front edge of the feltcovered strip 50, may conveniently be closed at each end by means of aside member such as 5.2 which is secured to the doctor blade.

The tension with which the clips 5| hold the trough in the describedrelation to the doctor blade is not suificient to prevent the troughfrom maintaining its described supporting engagement with the surface ofthe band Iii, notwithstanding any vertical adjustment of the doctorblade. The weight of the trough and its contents is sufiicient to causethe trough to remain stationary when the doctor blade is adjusted up ordown, the clips slipping vertically over the respective end portions ofthe trough.

It will be apparent that because of the small exposed area of the poolof liquid in the trough 38, the loss of solvents by evaporation from thetrough will be held to a minimum. It may be further reduced by applyinga cover to the trough if desired, and in the formation of sheeting fromcertain types of solution, for example from a vinyl resin solution, ithas been found that a sheet or film of the material will be formedacross the top of the pool extending from the forward edge of the topwall 43 to the doctor blade and from end to end of the trough. Theformation of such a film is, of course, aided by the small extent of thearea to be covered. In one practical embodiment of the structure, thedimension of the film between the trough and the doctor blade is between1 and 2 inches, and in that case the formation of the covering film asreferred to has been found to occur very quickly after the apparatus isset in operation. The formation of such film effectively seals thetrough against further evaporation of solvents, and hence insuresdelivery of the solution in the desired condition to the forming bandID.

On the front upper portion of the doctor blade 2 there is fixedlymounted a wood or other suitable bar 53, the same being secured byscrews or otherwise directly to the blade 24. An adjustably mounted bar55, also of wood or other suitable material, is associated with thelower front portion of the doctor blade so as to cooperate with thebeveled face 35 of the latter to form a chamber 55. The bar 54 may bevertically adjustably connected to the upper bar 53 by means of anadjusting screw 55, which has its threaded end threaded into an anglemember 51 secured to the bar 54 and its upper end rotatably anchored inan angle bracket 58 which is secured to the upper bar 53. It will beapparent that by appropriately rotatin the screw 56, the bar 54 may beadjusted up or down to thereby regulate the position of the lower edge59 of said bar 54 with reference to the band In and the coating Lthereon. Suitable bowed springs, such as indicated at 60, may beemployed for resiliently holding the lower bar 54 in place against thefront face of the doctor blade 24. Such bowed springs 60 may be securedto the upper bar 53 by means of screws such as indicated at 6!, by meansof which the pressure of the springs 68 on the bar 54 may be adjusted.

The chamber 55 may be closed at its ends by suitable means such asplates 52 secured to the ends of the doctor blade. Said chamber servesto entrap some of the solvent of the liquid solution to thereby preventstarting of the drying process until the liquid coating on the band hashad an opportunity to achieve a smooth, non-wavy surface, which ishighly desirable in the formation of most sheeting. Specifically, thesolvent retaining chamber 55 appears to provide the required timeinterval for the smoothing out of ripples which would otherwise appearon the surface of the liquid coating incident to the passage of theunquid under the lower edge of the doctor blade. This feature isparticularly important in connection with the formation of sheeting fromliquid which embodies a highly volatile solvent and which tends to takea surface set almost immediately upon exposure to air. In the drawings,particularly in Fig. 3, the thickness of the band i0 and the depth ofthe liquid coating L are considerably exaggerated for purposes ofillustration, and it will be understood that the depth of the liquidcoating is usually only a matter of a few thousandths of an inch, sothat the tendency of certain liquids to set rapidly is pronounced.

In one example of the production of sheeting from one vinyl resinsolution, the solution is preferably delivered to the trough at atemperature of about F. In order to maintain the pool of the solution inthe trough at the selected temperature, hot water or other medium at therequired temperature, for example at F1, may be circulated through thejacket 39. Such heating medium may be derived from any suitable source.Owing to the small body of solution which requires temperature control,a relatively small water jacket is required. Due to the relatively smallsize of the doctor blade 24, heat loss through that source is held downto a practical minimum so that the temperature controlling medium neednot be heated to an excessively higher temperature than the desiredtemperature of the solution.

The vertical plane of the rear face of the doctor blade, and hence thevertical plane in which lies the operative edge 3'! of the doctor blade,is preferably disposed slightly rearwardly of the vertical plane of theaxis of the drum H. By this arrangement the doctor blade edge 31 will bein operative relation to a portion of the band which is firmly supportedby the drum and incapable of any material wavering therefrom which couldimpair the constancy of the space between the doctor blade edge 31 andthe surface of the band As represented in Figure l, the band I!) carriesthe liquid coating from the casting or forming apparatus into an oven rdryer 63 of any suitable construction. Upon emergence of the sheetcovered band from the dryer, the sheeting may be stripped from the bandby any preferred mechanism so as to leave the band clean and free forcontinuation of the film casting operation. By circulating a heatingmedium through the drum ll, the temperature of the band is effectivelycontrolled so that the liquid solution will not be congealed or frozenupon contact with the band but will retain its free flowing liquid formlong enough for the proper formation of the sheet producing coating.

Changes in the described structure may be made without departing fromthe principles of the invention as above described and referred to inthe appended claims.

I claim:

1. In film forming apparatus of the class described, the combination ofan endless belt on which to form a film from a liquid solution, a doctorblade, means supporting said doctor blade, said means being adjustableso as to permit adjustment of the doctor blade toward and from saidmoving member, a trough for delivering the film forming solution to saidendless belt, means for supporting said trough on said endless belt, andmeans carried by said doctor blade for slidably holding said troughagainst said doctor blade, said means permitting said doctor blade to bevertically adjusted while said trough remains supported on said endlessbelt.

2. Apparatus according to claim 1 wherein the means for supporting thetrough on the endless belt comprises non-scratching means detachablysecured to the bottom of said trough and engaging the film formingsurface of said endless belt.

3. Apparatus according to claim 1 in which the means for supporting saidtrough on said endless belt comprises a cloth-covered strip detachablysecured to the bottom of said trough.

4. In apparatus for forming a sheet from a liquid solution, a movingmember having a surface to which the solution is delivered, a doctorblade having its lower edge spaced from said surface and co-operatingtherewith to determine the thickness of the film of solution carriedpast said doctor blade by said moving member, said lower edge having asubstantially straight central longitudinal portion and elongated endportions extending downwardly and outwardly from said central portion tothereby efifect tapering of the marginal portions of the sheet formingsolution passing under said edge, whereby the normal tendency of thefilm to build up its marginal thickness is counteracted and uniformityof sheet thickness is attained.

5. In apparatus for forming a sheet from a liquid solution, a movingmember having a surface to which the solution is delivered, a doctorblade having its lower edge spaced from said surface and co-operatingtherewith to determine the thickness of the film of solution carriedpast said doctor blade by said moving member, said lower edge having asubstantially straight central longitudinal portion and elongated endportions extending downwardly and outwardly from said central portion tothereby efi'ect tapering of the marginal portions of the sheet formingsolution passing under said edge, whereby the normal tendency of thefilm to build up its marginal thickness is counteracted and uniformityof sheet thickness is attained, said doctor blade having at least suchlower edge portion formed of an alloy which is substantiallynon-expansible within the normal range of temperatures encountered inthe sheet-forming operation.

EDOUARD M. KRATZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 864,028 Peters Aug. 20, 19071,764,423 Stone June 1'7, 1930 410,898 Kattentidt Sept. 10, 18891,604,941 Hofmann Oct. 26, 1926 171,629 Owens Dec. 28, 1875 953,570Zickerman Mar. 29, 1910 2 ,033,379 Jenkins et al Mar. 10, 1936 1,829,153Pearl Oct. 27, 1931 328,958 Maxfield Oct. 27, 1885 1,033,282 SleeperJuly 23, 1912 2,261,411 Rees Nov.-4, 1941 2,051,201 Davidson Apr. 18,1936 1,961,025 Wickham May 29, 1934 2,011,354 Carver et al. Aug. 13,1935

